Cycle For Hydrogen Production Research Articles

Safety Analysis of the Hydrolysis Reactor in the Cu-Cl Thermochemical Hydrogen Production Cycle—Part 1: Methodology and Selected Top Events

In this paper, IEC 61511 was used to evaluate the hazards and risks associated with the continuous operation of the hydrolysis reactor system in the copper-chlorine thermochemical hydrogen production cycle, with a specific focus on the application of automated active safety systems and safety integrated systems. The analysis presented herein was performed using a speculative but representative hydrolysis piping and instrumentation diagram (P&ID) for the hydrolysis reaction, which was based on currently published systems as well as experience with experimental hydrolysis reactors. This analysis was then used to inform the design of a set of automated safety systems that provide the redundant operation of critical devices and can bring the hydrolysis to a safe shutdown state if needed.

Thermodynamic and environmental performance of a Kalina-based multigeneration cycle with biomass ancillary firing for power, water and hydrogen production

The performance of a Kalina-based multigeneration cycle for power, water, and hydrogen production is investigated from thermo-environmental, sustainability, and thermo-economic perspectives. The plant comprises a gas turbine (GT), Kalina cycle (KC), and vapor absorption system (VAS) as the bottoming cycle and an integrated domestic water heater and proton-electron membrane (PEM) electrolyzer for hydrogen production. The system's models were simulated with Engineering Equation Solver (EES) codes. The results indicate a net energy efficiency of 53.48% and exergy efficiencies of 50.05 %, with an additional 30,178 kW of products from the bottoming cycles. The GT contributed approximately 85.81 % of the overall exergy destruction. The system's exergo-thermal index (ETI) stood at 1.713, with the GT only having an ETI of 2.106. Similarly, the exergetic sustainability index (ESI) of the multigeneration plant was not greater than 2.04. The exergoeconomic analysis shows a low average energy cost from the GT, estimated at 0.836 $/GJ, compared to the Kalina subsystem, which stood at 6.53 $/GJ. The thermodynamic and cost evaluation of the system demonstrates substantial benefits from the plant, which kept the hydrogen production rate at 0.1524 kg/hr.

Experimental study and modelling of continuous SO2-depolarized electrolysis in hybrid sulfur cycle for hydrogen production

SO2-depolarized electrolysis (SDE) is the key process in the hybrid sulfur cycle for green hydrogen production, but the detailed SDE characteristics including products generation, current efficiency variation, and side reactions are unclear. Herein, a continuous SDE process was experimentally conducted and theoretically modelled. The H2 and H2SO4 production was accelerated and the current efficiency for both electrodes was improved with a proper increase in current density (50−100 mA/cm2) or temperature (293−318 K), but further increasing current density to 150 mA/cm2 or temperature to 333 K led to a negative trend because of the anode corrosion or declined SO2 solubility. The increasing initial H2SO4 concentration (10−40 wt%) facilitated the cathodic H2 production and current efficiency, while negatively influenced the anodic SO2 conversion. The parasitic reactions occurred at cathode consumed H2 and resulted to the cathodic current efficiency well below 100%. A rigorous mathematical regression model correlating the production rates of H2 and H2SO4 with current density, temperature, and initial H2SO4 concentration was developed, and combined with the analysis of variance, current density was suggested the biggest factor affecting products generation in SDE process. These findings demonstrate a practical avenue for efficient SO2 conversion and H2 production in SDE process of hybrid sulfur cycle.

Chemistry of the iron-chlorine thermochemical cycle for hydrogen production utilizing industrial waste heat

This research presents an inventive thermochemical cycle that utilizes a reaction between iron and HCl acid for hydrogen production. The reaction occurs spontaneously at room temperature, yielding hydrogen and a FeCl2 solution as a by-product. Exploring the thermal decomposition of the FeCl2 by-product revealed that, at conditions suitable for utilization of low-temperature industrial waste heat (250 °C), chlorine gas formation can be circumvented. Instead, the resulting by-product is HCl, which is readily soluble in water, facilitating direct reuse in subsequent cycles. The utilization of low-temperature industrial heat not only optimizes resource utilization and reduces operational costs but also aligns with environmentally sustainable production processes. From the kinetic studies the activation energy was calculated to be 45 kJ/mol and kinetics curves were constructed. They showed significant kinetics at room temperature and above but rapid decrease towards lower temperatures. This is important to consider during real-scale technology optimization. The theoretical overall energy efficiency of the cycle, with 100% and 70% heat recuperation, was calculated at 68.8% and 44.8%, respectively. In practical implementation, considering the efficiency of DRI iron reduction technology and free waste heat utilization, the cycle achieved a 41.7% efficiency. Beyond its energy storage capabilities, the Iron-chlorine cycle addresses safety concerns associated with large-scale hydrogen storage, eliminating self-discharge, reducing land usage, and employing cost-effective storage materials. This technology not only facilitates seasonal energy storage but also establishes solid-state energy reserves, making it suitable for balancing grid demands during winter months using excess renewable energy accumulated in the summer.

Continuous multiphase Bunsen reactor of iodine-sulfur thermochemical water splitting cycles for hydrogen production: Experimental, Modelling and Design Insights

Thermochemical water splitting cycles (TWSCs) hold promise for sustainable H2 production in future energy systems, with Iodine-Sulfur (IS) and Nickel-Iodine-Sulfur (NIS) processes standing out as efficient options. The core of both these processes lies in the Bunsen reaction, underscoring the need to identify optimal operational conditions and plant solutions for this crucial reaction section. Thus, in this study, a continuous counter-current flow Bunsen reactor fed with 5 NL h−1 of SO2 was constructed and tested. An inventive aspect was the introduction of solid I2 pellets from the top to enhance saturation at the liquid-liquid interface between sulfuric and hydriodic product phases, promoting segregation. This ingenious design achieved nearly complete SO2 conversion and optimal H2SO4 and HI concentrations in the respective product phases, while avoiding undesirable byproduct formation. The study further advanced the modelling of the experimental reactor by employing innovative kinetic and liquid-liquid equilibrium description approaches, and demonstrating exceptional validation accuracy of R2 = 0.9988. Additionally, with the aim of obtaining design charts as a potential tool for Bunsen reactor design, a microscopic model describing the gas phase trend along bubble or packed Bunsen-type reactors was developed. The model’s dimensionless analysis revealed a characteristic times ratio (Bu) comprehensively describing all the phenomena occurring to the gas phase within the Bunsen reaction section, and identified an optimal Bu value of 0.4 for pure SO2 gas inlet. Overall, the study's innovative strategies and models contribute significantly to the advancement of Bunsen reactor engineering.

Thermodynamic analysis on CSP integrated cerium oxide (CeO2 − CeO1.72/1.83) water splitting cycle for hydrogen production

Solar thermochemical CeO2-based H2O splitting cycle was thermodynamically analyzed to ascertain the optimal thermal reduction (TH) and re-oxidation (TL) temperatures and evaluate the solar-to-fuel conversion efficiency (ηsolar−to−fuel) of the cycle. The equilibrium composition of CeO2, CeO1.72,CeO1.83 and O2 exhibited that the thermal reduction initiated at 1400 K thereby attaining 100 % TR at 2734 K. The observed variations in Gibbs free energy (ΔG) correspond to the feasibility of the re-oxidation step of CeO1.83 and CeO1.72 at 1050 K and 1200 K respectively. It was reported that the absorption efficiency of solar reactor (ηabs−solar−reactor−WS) decreases from 95.6 % to 37 %, as the TH increases from 1400 K to 2734 K. The results show that ηsolar−to−fuel reached the maximum value of 7.45 % for CeO1.72 and 7.69 % for CeO1.83 at 61.72 % TR of CeO2 without heat recuperation. Further, the ηsolar−to−fuel attained the maximum value of 14.92 % and 13.54 % for CeO1.83 and CeO1.72, respectively at the %TR of CeO2 of 80 % with 50 % heat recuperation. The solar-to-fuel conversion efficiency (ηsolar−to−fuel) further can be increased with the optimization of oxygen partial pressure (PO2) and molar flow rate of reduction regents (Ar or N2).

HI decomposition over the HI-100 test apparatus at a hydrogen production rate over 100 L/h

Studies on the iodine-sulfur (IS) thermochemical cycle for hydrogen production has been carried out since about 2005 by the Institute of Nuclear and New Energy Technology, Tsinghua University, China. The HI decomposition occupies the important position of hydrogen generation in the IS cycle. In this paper, the HI-100 test apparatus with a H2 production rate of 100 L/h was constructed and the HI decomposition was tested. First, the process and components for HI decomposition were designed. Then, the key components, including the feed tank, evaporator, gas heater, adiabatic reactor, condenser, and gas-liquid separator were made of industrial materials. After building this apparatus, the sealing test, heating water test, and HI decomposition have been conducted. The stable hydrogen production operation of more than 100 L/h had been achieved for 5 h, the maximum hydrogen production reached approximately 130 L/h, and the hydroiodic acid decomposition rate maintained about 22 %. The test results provide the design and experimental guidance for further amplification of HI decomposition for hydrogen production by the IS cycle.

Process modelling and assessment of thermochemical sulfur-iodine cycle for hydrogen production considering Bunsen reaction kinetics

Thermochemical sulfur-iodine (SI) cycle is one of the large-scale, clean, and efficient hydrogen production routes. The Bunsen reaction process is always simulated by a stoichiometric reaction, without considering the realistic Bunsen reaction kinetic process. Herein, a user-defined Fortran module concerning Bunsen reaction kinetics was developed and embedded into a continuous stirred tank reactor (RCSTR), and then a SI flowsheet with 100 L/h hydrogen production was modeled. The key parameter optimization, mass and energy balance were analyzed, the internal heat exchange network was created using the pinch point temperature difference analysis and the principle of energy cascade utilization, along with thermal efficiency evaluation. Bunsen reaction process reaches equilibrium after a period, which is consistent with experiments. The increase of H2SO4 decomposition ratio is beneficial to reduce the energy consumption of system. Increase in temperature has less effect on increasing the equilibrium decomposition ratio of HI. The theoretical thermal efficiency of system reaches 14.0–57.4 % considering the recovery of exothermic heat. This work provides a theoretical basis for the optimization of SI cycle.

Evaluating the influence of Ar/N2 flow rate and pressure on the conversion efficiency of a solar-assisted Fe2O3 – FeO WS cycle for hydrogen production: A thermodynamic approach

A thermodynamic analysis is carried out to evaluate the effects of oxygen partial pressure (PO2) and molar flow rate of reduction agents (m˙N2/Ar) on the performance of Fe2O3−FeO solar thermochemical cycle (STC|Fe2O3−FeO). The chemical equilibrium and efficiency analysis parameters such as enthalpy, Gibbs free energy and entropy are calculated as a function of thermal dissociation temperature (TH). The chemical equilibrium analysis suggests that the thermal dissociation step is feasible above 1250 K while the re-oxidation step is practicable at 550 K. The efficiency analysis revealed that the highest value of conversion efficiency (ηsolar−to−fuel) reached up to 44.42% for N2 based cycle and 45.46% for Ar based cycle without using the recuperation technique. However, the conversion efficiency (ηsolar−to−fuel) attained the highest value of 57.84% for N2 based cycle and 59.14% for Ar based cycle with 50% heat recuperation.

Molten salt heat exchanger design for the thermolysis reactor in the Cu–Cl cycle of hydrogen production

The thermochemical copper–chlorine (Cu–Cl) cycle is known as a promising method for producing clean hydrogen. Due to the high-temperature environment of the thermolysis reactor, there are commercialization challenges with regard to the heat exchanger design. In this study, a new design for the heat exchanger used in the thermolysis reactor of a 4-step Cu–Cl cycle is presented, aiming to achieve the required temperature distribution of 430 °C–550 °C. A design methodology is developed for the heat exchanger along with an iterative algorithm for the sizing problem. The final design of this study has decreased the T* (representative of the temperature range) by 51 % compared to the previous designs, with the improvement techniques resulting in increasing the heat exchanger effectiveness and thermal performance factor by 15 % and 138 % and decreasing average TD (representative of the temperature dispersal) by 61 %. The achieved operating temperature ranges from 431.3 °C to 539.0 °C.

Thermodynamic assessment of thermochemical cycle for hydrogen production based on water decomposition with binary copper chlorine couple

Thermodynamic assessment of thermochemical cycle for hydrogen production based on water decomposition with binary copper chlorine couple

Performance analysis of a small lead-cooled fast reactor coupled with a copper-chloride cycle hydrogen production system

Hydrogen is widely acknowledged as a pivotal energy carrier in the global transition towards sustainable energy. One promising approach to hydrogen production is method copper-chlorine cycle powered by nuclear energy. This article presents an innovative integrated system for small lead-cooled fast reactors that are coupled with a copper-chlorine cycle. To assess the performance of the entire system with regards to energy, exergy, and economics, comprehensive modeling, simulation, and analysis are conducted using the simulation tool Simulink. Furthermore, a comprehensive examination of key operating parameters was conducted to explore their impact on the system. The obtained results demonstrate the energy efficiency of system is 21.3 % and the exergy efficiency of system is 40.9 %. The overall system based on the small LFR can produce high-pressure compressed hydrogen gas at a rate of 2.34 g/s and generate 53.9 kW of electricity. According to the study, the levelized cost of energy production is determined to be $0.04252/kW·h. The specific energy cost is primarily influenced by equipment investment, including the costs associated with operating and maintaining the system. Notably, the small lead-cooled fast reactor and the copper-chlorine cycle plant represent the major capital investments within the system. This study provides valuable insights and serves as a significant reference for the future engineering applications of lead-cooled fast reactors coupled with copper-chlorine cycle hydrogen systems.

Developing and optimizing a new cogeneration cycle to produce hydrogen from seawater

Global warming and the depletion of fossil fuels have driven countries to develop alternative fuel strategies. As an alternative fuel, hydrogen is very attractive since it has a high thermal energy and near-zero emissions. This paper proposes a new arrangement of the cogeneration cycle for hydrogen production from seawater is proposed and optimized via the multi-objective swarm optimization (MOPSO) algorithm. In this survey, hydrogen is produced through the electrochemical cycle Copper-Chloride (Cu-Cl), using the heat and electricity provided via waste heat recovery of a gas cycle. A reverse osmosis system provides drinking water for the Cu-Cl cycle. This cycle can produce 256 GWh of electricity and 23616 tons/year of hydrogen during a year. This cycle's first and second law efficiencies are 35.3 % and 7.2 %. Based on the financial aspects, this cycle's investment return time equals 4.1 years. By using MOPSO algorithm, the exergy efficiency of the cogeneration system is improved by 22.7 %, while the payback is decreased by around 33.3 %.

Corrosion behavior of SiC coated HX with MoSi2 interlayer to be utilized in iodine–sulfur cycle for hydrogen production

In this era, renewable energy technologies are suitable to meet the challenges of fossil fuel depletion and global warming. Thus, hydrogen is gaining attention as an alternative clean energy carrier that can be produced from various methods, one of them is the iodine-sulfur (I–S) cycle which is a thermochemical process. The I–S cycle requires a material that can withstand an extremely corrosive environment at high temperatures. Immersion tests were conducted on bare superalloy Hastelloy X (HX), MoSi2, and SiC–MoSi2 coated HX, deposited in physical vapor deposition (PVD) to evaluate their corrosion resistance. Bare HX exhibited a high corrosion rate of 208.1 mm yr−1 when exposed to 98 wt% sulfuric acid at 300 °C. In contrast, HX with MoSi2 coating showed a much lower corrosion rate of 23.5 mm yr−1, and HX with SiC–MoSi2 coating demonstrated the lowest corrosion rate at 6.5 mm yr−1 under the same conditions. The coated samples were analyzed via FESEM before and after corrosion testing. The FESEM images reveal the formation of coalescent particles on the surface of the coating. The elemental analysis illustrates an increased concentration of silicon and oxygen in the corroded samples. Elemental mapping of these samples show a uniform distribution of elements over the sample. These findings contribute not only to materials science understanding but also to practical applications in hydrogen production via the I–S cycle, where corrosion-resistant materials are critical.

A comparative analysis of integrating thermochemical oxygen pumping in water-splitting redox cycles for hydrogen production

Solar thermochemical hydrogen (STCH) is a promising route for renewable fuel production, but efficiency and cost concerns must be addressed before it can contribute meaningfully to decarbonization efforts. The oxygen removal (reduction) step of two-step STCH redox cycles needs high temperature (1300–1500 °C) and low oxygen partial pressure (10-5-10-3 bar). This consumes significant energy by way of redox reheating, re-radiation losses and pumping work. Thermochemical oxygen pumping (TcOP) has been shown to be more efficient than mechanical pumps in the medium vacuum range, enabling higher heat-to-fuel efficiency and potentially lower reduction temperatures. We have previously proposed a novel Reactor Train System for STCH and reported significant efficiency and productivity improvements by replacing mechanical pumps with TcOP. The current work is a comparative analysis of different implementations of TcOP and its hybridization with conventional oxygen removal schemes like mechanical vacuum pumps and inert gas sweep. The integration of these hybrid TcOP systems with different STCH reactor systems using redox monoliths or particles is analyzed in terms of energy use along with mass and heat transfer considerations. Our results show that direct oxygen transfer between STCH and TcOP reactors results in the best performance for reduction oxygen partial pressures below 10 Pa. Furthermore, we show that achieving reduction pressures of 1 Pa and lower is challenging with existing reactor systems due to a combination of low gas density and relatively high molar flowrates. This challenge also applies to other oxygen removal systems like vacuum pumps and inert sweep.

Synthesis and testing of NixZn1-xFe2O4/CNTs photoresponsive magnetic composite catalysts for hydrogen generation from water splitting

The world is facing environmental pollution and energy shortage challenges due to the enormous wastage of organic pollutants by industries and the rapid growth of the human population. Photocatalysis has been reported as an efficient technology to mitigate these two emerging issues. This study investigated heterojunction photocatalysts based on NixZn1-xFe2O4/CNTs for enhanced H2 production from water splitting. The role of CNTs in accepting electrons during redox reactions, improving the photocatalytic activity and stability of NiZnFe2O4, and reducing the recombination of charge carriers is also elaborated in this study. The synthesized NixZn1-xFe2O4/CNTs composites were characterized using several methods, including SEM, EDX, FTIR, XRD, and UV–Vis-DRS to examine their magnetic electrical, opto-physical, and photocatalytic activity. The maximum hydrogen evolution rate of 4550 μmolh−1g−1 was observed using N0.4Z0.6FC0.3, which is 5 and 2.3 times greater than that of NZF and Ni0.1Zn0.9FC0.3 catalysts, respectively. The successive cycles of hydrogen production using N0.4Z0.6FC0.3 showed strong stability and reusability of this catalyst. The photocatalytic mechanism of water splitting using NixZn1-xFe2O4/CNTs photocatalysts is also deduced in this study.

Decoupling the anodic and cathodic behavior in asymmetric electrochemical hydroiodic acid decomposition cell for hydrogen production in the iodine-sulfur thermochemical cycle.

The HI section of the iodine-sulfur (I-S) thermochemical cycle for hydrogen production is one of the most energy-intensive sections and with significant material handling challenges, primarily due to the azeotrope formation and the corrosive nature of the hydroiodic acid-iodine-water mixture (HIx). As an alternative, the single-step direct electrochemical decomposition of the hydroiodic acid (HI) to generate hydrogen can circumvent the challenges associated with the conventional multistep HI section in the I-S cycle. In this work, we present new insights into the electrochemical HI decomposition process by deconvoluting the contributions from the anodic and the cathodic sections in the electrochemical cell system, specifically, the redox reactions involved and the overpotential contribution of the individual sections (anolyte and catholyte) in the overall performance. The studies on the redox reactions indicate that the HIx solution output from the Bunsen reaction section should be used as the anolyte. In contrast, aqueous HI without any iodine (I2) should be used as the catholyte. In the anodic section, the oxidation proceeds with I2 as the final oxidized species at low bias potentials. Higher positive potentials result in iodate formation along with oxygen evolution. For the catholyte section, I2 and tri-iodide ion reduction precede the hydrogen evolution reaction when I2 is present along with HI. Furthermore, the potential required for hydrogen production becomes more negative with an increasing I2/HI ratio in the catholyte. Polarization studies were conducted with simultaneous deconvolution of the anodic and cathodic behavior in a two-compartment cell. Model fitting of the polarization data revealed that the anolyte section's activation overpotential is negligibly low. In contrast, the activation overpotential requirement of the catholyte section is higher and dictates the onset of hydrogen production in the cell. Furthermore, the catholyte section dominates the total overpotential losses in the cell system. Operation in the ohmic resistance-dominated zone resulted in close to 90% current efficiency for the electrochemical HI decomposition. The results highlight that the potential for process improvement lies in reducing the ohmic resistance of the anolyte section and in lowering the activation overpotential of hydrogen evolution in the catholyte section.

Enhanced photocatalytic hydrogen production from Co-MOF/CN by nitrogen and sulfur co-doped coal-based carbon quantum dots

A novel composite photocatalyst for photocatalytic decomposition of water for hydrogen evolution was successfully synthesized by in-situ growth of nitrogen and sulfur co-doped coal-based carbon quantum dots (NSCQDs) nanoparticles on the surface of sheet cobalt-based metal-organic framework (Co-MOF) and graphitic carbon nitride (g-C3N4, CN). The structure and properties of the obtained catalysts were systematically analyzed. NSCQDs effectively broaden the absorption of Co-MOF and CN in the visible region. The new composite photocatalyst has high hydrogen production activity and the hydrogen production rate reaches 6254 μmol/(g·h) at pH = 9. At the same time, NSCQDs synergy Co-MOF/CN composites have good stability. After four cycles of hydrogen production, the performance remains relatively stable. The transient photocurrent response and Nyquist plot experimental results further demonstrate the improvement of carrier separation efficiency in composite catalysts. The semiconductor type (n-type semiconductor) of the single-phase catalyst was determined by the Mott–Schottky test, and the band structure was analyzed. The conductive and valence bands of CN are −0.99 and 1.72 eV, respectively, and the conduction and valence bands of Co-MOF are −1.85 and 1.33 eV, respectively. The mechanism of the photocatalytic reaction can be inferred, that is, Z-type heterojunction is formed between CN and Co-MOF, and NSCQDs was used as cocatalyst.

Insights into the stability of the iron oxide immobilized into mesoporous silica catalysts in iodine–sulfur cycle for hydrogen production

Insights into the stability of the iron oxide immobilized into mesoporous silica catalysts in iodine–sulfur cycle for hydrogen production

Enhanced morphological maintenance and redox stability by dispersing nickel ferrite into silica matrix for chemical looping hydrogen production via water splitting

Chemical looping hydrogen production (CLHP) is widely regarded as a clean and efficient route for high purity hydrogen production. However, a huge barrier is how to avoid serious deactivation caused by sintering and agglomeration of oxygen carriers. A novel fabrication process of highly dispersing NiFe2O4 into silica matrix is proposed. The oxygen carriers of NiFe2O4 completely dispersed over silica matrix (NFSM) are successfully synthesized. The characterizations, hydrogen production capacity and cycle redox performance of oxygen carriers are further investigated. The results illustrate that NiFe2O4 active components are homogeneously dispersed on the silica matrix without any impurities. NFSM demonstrates the highest reactivity with CO as well as the greatest hydrogen production of 296 mL/g due to the strong confinement effect of silica matrix and good particle dispersion. The porous silica matrix offers large amounts of channels for the lattice oxygen transport and effectively prevents Fe and Ni cations outward migration to particle surface, which actually inhibits the larger clusters and sintering. NFSM can keep stable hydrogen production of approximately 290 mL/g during the cyclic experiments. Briefly, the innovation method of embedding active component into well-established silica matrix supports contributes to the enhanced anti-sintering properties and redox stability of oxygen carriers.